The present invention relates to the measurement of pipeline corrosion, and in particular, to a laser mapping apparatus and method for evaluating external and internal pipeline corrosion.
Pipeline maintenance requires early and accurate detection of external corrosion in buried steel pipe. External corrosion detection is, initially, typically conducted from within the pipeline using in-line inspection vehicles (e.g. smart pigs) or from outside the pipeline using equipment to detect the leakage of cathodic protection current. Smart pigs typically utilize either magnetic flux leakage, eddy current or ultrasonic technology, or a combination thereof. After removal of scale by water blasting and other techniques, external corrosion is typically further evaluated by visual inspection.
Once an area of corrosion has been detected, corrosion measurement and evaluation follow. Typically, the pipeline is excavated and grit blasted in the area of corrosion in preparation for more accurate measurement of corrosion and pitting. There are several methods for manually measuring pitting, some using simple instruments such as pit gauges, scale and straight edge, wire contour gauges, and bridging bars with micrometers, and others using complex equipment such as ultrasonic detectors and radiographic equipment, all of which have their disadvantages.
Internal corrosion is evaluated using similar techniques, with cleaning, inspection and measurement techniques limited by the accessibility and purpose of the pipe, and type of material carried by the pipe.
Regardless of which surface of the pipeline is evaluated, once the effected area has been measured and depth of pits therein determined, the remaining wall thickness and strength of the corroded pipe is evaluated using one of several available algorithms. Informed decisions can then made whether to repair or replace the corroded section of pipe or allow it to remain in service.
Although generally effective, known methods and equipment for measuring pitting have several drawbacks. For example, known methods are performed primarily in a longitudinal direction along straight pipe sections, obviating desirable evaluation of elbows, bends and curved circumferential portions of pipe surfaces. In addition, existing corrosion measurement instruments have mechanical limitations which further restrict measurement of corrosion to small areas or points. As a result, evaluation of a larger area requires continual movement of instruments in two dimensions to establish a grid of data, and such movement introduces errors in the data. Thus, known methods typically obtain data whose accuracy and resolution is low. Where pipe diameters prevent entry, access to internal surfaces is limited to surfaces near openings.
Complex corrosion measurement instruments have further drawbacks. In particular, ultrasonic detectors, although accurate for point measurement, require transducer access to the bottom of the pit or fluid coupling of the transducer and pipe, making it very messy for evaluation of excavated pipes. Radiographic equipment presents an x-ray hazard to operators, and films produced require further time and equipment for development and analysis. Moreover, while radiography is good for qualitative detection of corrosion, it is not an accurate technique for quantitative measurement of corrosion. As a result, known methods for corrosion measurement are not only mechanically limited, but are also expensive and time consuming because of the labor involved to perform the method, process data, and interpret the results.
Accordingly, the need exists for a cost-effective automatic corrosion analysis apparatus and method which enables rapid measurement and evaluation of significant portions of both straight and curved corroded pipe sections.